Anycalculator Ohm's Law Calculator

Enter 2 amounts, then click answer button.

Voltage millivolts volts kilovolts megavolts
Current milliamps amps kiloamps megaamps
Resistance milliohms ohms kilohms megaohms
Power milliwatts watts kilowatts megawatts

The law stating that the direct current flowing in a conductor is directly proportional to the potential difference between its ends. It is usually formulated as V = IR, where V is the potential difference, or voltage, I is the current, and R is the resistance of the conductor.

Ohm's Law

Following are the formulas for computing voltage, current, resistance and power. Traditionally, E is used for voltage (energy), but V is often substituted.

V or E = voltage (E=energy)
I = current in amps (I=intensity)
R = resistance in ohms
P = power in watts

V = I * R E = I * R

I = V / R I = E / R

R = V / I R = E / I

P = V * I P = E * I


Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. he law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire.

Ohm's law was probably the most important of the early quantitative descriptions of the physics of electricity. We consider it almost obvious today. When Ohm first published his work, this was not the case. Ohm's law remains correct for the average current, in the case of ordinary resistive materials.

Resistors are circuit elements that impede the passage of electric charge in agreement with Ohm's law, and are designed to have a specific resistance value R.

Ohm's law holds for circuits containing only resistive elements (no capacitances or inductances) for all forms of driving voltage or current, regardless of whether the driving voltage or current is constant (DC) or time-varying such as (AC). At any instant of time Ohm's law is valid for such circuits.

Resistors which are in series or in parallel may be grouped together into a single "equivalent resistance" in order to apply Ohm's law in analyzing the circuit.

Note: Resistance cannot be measured in an operating circuit, so Ohm’s Law is especially useful when it needs to be calculated. Rather than shutting off the circuit to measure resistance, a technician ie an ET, can determine R using the above variation of Ohm’s Law.

Now, if you know voltage (E) and resistance (R) and want to know current (I), Divide (E) by (R)   (see the equation above).

And if you know current (I) and resistance (R) and want to know voltage (E), multiply (I) x (R)  (see the equation above) .

If you know voltage (V) and current (I) and want to know resistace (R), divide (E) by (I)  (see the equation above) .

Circuits, like all matter, are made of atoms. Atoms consist of subatomic particles:

Atoms remain bound together by forces of attraction between an atom’s nucleus and electrons in its outer shell. When influenced by voltage, atoms in a circuit begin to reform and their components exert a potential of attraction known as a potential difference. Mutually attracted loose electrons move toward protons, creating a flow of electrons (current). Any material in the circuit that restricts this flow is considered resistance.

What keeps the forces that bind all matter together? What keeps them constant? Click on the links below and find out from

Subatomic Particles, Part 1: Leptons

Subatomic Particles, Part 2: Baryons, the Substance of the Cosmos

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